1. In March of 1861, both houses of the US Congress passed the Corwin Amendment, a bill proposing a constitutional amendment that would protect slavery. President Buchanan signed the bill*, which then went to the several states for ratification.
Some yankee states, and even free yankee states, voted to ratify the bill, but none of the Confederate states (to include those that were still 'officially' part of the Union) so much as bothered to put the matter to a vote, effectively rejecting a proposal to enshrine slavery in the US Constitution.
https://en.wikipedia.org/wiki/Corwin_Amendment
2. The March 22, 1862 issue of Harper's Weekly reported that Lincoln had held out an olive branch to the Confederacy. Rejoin the Union -- no harm, ho foul -- and we'll abolish slavery incrementally and compensate slave owners for the loss.
No official from any southern state (Union or Confederate) rose to the bait, demonstrating again that slavery was not a motivation fundamental to secesion.
http://www.sonofthesouth.net/leefoundation/civil-war/1862/march/slavery-compromise.htm
3. In January of 1865, Confederate President Davis sent Duncan F. Kenner (possibly the biggest slave owner in the continent) as envoy to the heads of state of France and Great Britain. Kenner was to attempt to enlist support for the Confederate cause from the European powers, hoping at the very least that they could be enticed to officially recognize the independence of the Confederacy. With the authority of the Confederate cabinet, Kenner was empowered to offer that in return for the Europeans' suppport, once the war was at a conclusion, the newly independent Confederate States would abolish slavery within a period of five years.
The French Emperor Napoleon Bonaparte III was willing to acknowledge the Confederacy, but only if the British Prime Minister would do the same. Prime Minister Henry John Temple refused to even meet with Kenner, which scuppered the deal. But even if Kenner had succeeded, his mission probably took place too shortly before Lee's surrender at Appomattox to have changed the outcome of the war.
Still, it shows the Confederacy was willing to throw a "Hail Mary" pass to get shut of Lincoln, even at the cost of slavery.
https://libertyclassroom.com/slavery-and-the-civil-war-revisited/
* This bill has never been rescinded or overturned.
That was just the ex post facto rationalization for the destruction they caused.